Lubricant composition



United States Patent Ofilice ddldflld Patented Jan. 28, 1954 Thisinvention relates to a superior new lubricant composition. Moreparticularly, the invention is concerned with a novel polymer thickenedlubricant composition having an improved viscosity index and aremarkable resistance to shear degradation.

Constant effort is being made to produce lubricants which exhibitrelatively little change in viscosity over a wide range of temperatures.Thus, in any application where a lubricant is subject to use in widevariations of temperature, it is desirable that the lubricant have nottoo high a viscosity at the lower temperatures, nor too low a viscosityat the higher temperatures. For effective lubrication the oil must notbecome so viscous at the lower temperatures so as to impede starting andcause excessive wear, and not become so thin at the higher temperaturesso as to fail to provide adequate separation of the wearing surface.

With regard to lubricating oils, these desired viscositytemperaturecharacteristics may be obtained in some measure by the incorporation ofcertain synthetic products of large molecular size and comparativechemical inertness. These products are known as viscosity index (V.l.)improvers. However, any initial rise in V1. attributable to theincorporation of the high molecular weight product will diminish uponoperation of the machinery due to the shear forces set up by the movingparts of the machinery, for example, as in an internal combustionengine. These forces serve to shear the high molecular weight additiveinto component parts of lower molecular weight, yielding in turn a lowerV1. It can thus readily be seen that a high resistance to sheardegradation is an exceptionally desirable property of a lubricantcomposition. A further highly desirable propertly of a lubricantadditive composition is that a desired improvement in V.l. can beachieved by the addition to the lubricating oil of a small percent byweight of the additive.

It has now been found that lubricant compositions consisting of a majorproportion of an oil of lubricating viscosity and a minor proportion,sufficient to improve the viscosity index of said oil, of a novel classof oil-soluble high molecular weight polypeptides derived from esters ofoptically-active glutamic acid exhibit remarkably each of the abovedescribed highly desirable properties. These novel polypeptides providesurprisingly effective lubricant thickening at low concentrations.Further, these novel polypeptides display a highly remarkable resistanceto permanent shear degradation. his unusual combination of elfectivethickening power, low per cent by weight additive requirement, andexcellent shear strength, makes these novel poly eptides particularlydesirable and useful as V1. improvers.

The polypeptides of the present invention have the following generalformula:

where R is selected from the group consisting of benzyl radicals, andalkyl radicals containing from 8 to 18 carbon atoms. The benzyl radicalwill occupy from to 30 mol. percent of the ester radical (R) positionsand the alkyl radical will occupy from 70 to 100 mol. percent of theester radical positions. The molecular weight of the polymer will rangefrom 10,000 to 1,000,000 with n being the number of recurring unitsnecessarily corresponding to the molecular weight.

These polyesters may be suitably prepared by transesterification ofpolybenzyl glutamate with the appropriate alcohol, or by directsynthesis from the glutamate monomer. The following specific exampleswill serve to illustrate the preparation of the products of the presentinvention, in particular, polylauryl glutamate.

EXAMPLE I Trans-esterification of polybenzyl glutamate: A 14.49 g.quantity of poly-'y-benzyhL-glutamate is dissolved in 250 cc. of drychloroform. 170 cc. of dry lauryl alcohol is added with stirring andheating, along with 20 cc. of a mixture made from 7.86 g. of p-toluenesulfonic acid monohydrate and 600 cc. of benzene, wherein all water wasremoved by azeotroping. The mixture is refluxed for 48 hours, thereafterthe solution is kept at C. for six hours. At the end of this time nopolymer should precipitate upon the addition of isooctane. The polymeris now precipitated by pouring the solution into excess methanol andfiltering. The product is a white, fibrous polymer having a compositioncorresponding to 87% polylauryl glutamate and 13% polybenzyl glutamate,and having an estimated average molecular weight of about 150,000 asdetermined by viscosity measurements.

EXAMPLE II Direct synthesis from the glutamate monomer: g. of glutamicacid is suspended in a mixture of 1 liter of dry distilled laurylalcohol and 1 liter of sodium dried dioxane. 2.50 ml. of concentratedHCl (36%) is added and the mixture heated at 70 C. with stirring untilthe glutamic acid is dissolved. The solution is cooled to roomtemperature and diluted with 2 volumes of ether. After three hours, thecrystaliization of lauryl glutamate hydrochloride is complete. Thecrystals are filtered and washed with pentane. Yield, 43.5 g. of thehydrochloride as shimmering flakes. Then the anhydride is prepared bysuspending 60 g. of the hydrochloride in dry chloroform and bubblingphosgene through the refluxing solution with vigorous stirring until aclear solution is obtained (approx. six hours). After vacuum removal ofthe excess phosgene and solvent the residue is diluted with a dryn-heptane and the solution cooled to 0 C. Crystallization, initiated byscratching, is complete after 12 hours. After filtration the solution isrecrystallized at 30 C., collected and dried. Yield, 25 g. of theanhydride as colorless flakes. Polymerization is accomplished bydissolving 5 g. of the anhydride in 100 cc. of dry benzene and addnig0.1 cc. of a solution of 36 mg./cc. of triethylamine in dry benzene.After standing for 40 hours, the viscous solution is poured intomethanol and the precipitated polymer collected by filtration. Thepolylauryl glutamate product is a white, fibrous solid somewhat stickyto the touch. Yield, 95% completion of the reaction based upon theanhydride.

Calculated 68.63 10.51 4.10 Found 68.53 10.38 4.92

In general, excellent viscosity indexes can be imparted purpose ofpreparing a concentrate capable of dilution with lubricating oils andthe like to prepare the final lubricant composition. Such concentrates,which may also contain other additives in desired amounts, and whichnormally contain at least 10% of the polymer, comprise a convenientmethod for handling the polymer and may be used as a compounding agentfor lubricants in general.

The polymeric additives of this invention can be used with good effectin the ease of any one of a wide variety of oils of lubricatingviscosity, or of blends of such oils. Thus, the base oil can be arefined Pennsylvania or other parafifin base oil, a refined naphthenicbase oil, or a synthetic hydrocarbon or nonhydrocarbon oil oflubricating viscosity. As synthetic oils there can be allrylated waxesand similar alkylated hydrocarbons of relatively high molecular weight,hydrogenated polymers of hydrocarbons, and the condensation products ofchlorinated alkyl hydrocarbons with aryl compounds. Other suitable oilsare those which are obtained by polymerization of lower molecular weightalkylene oxides such as propylene and/ or ethylene oxide. Still othersynthetic oils are obtained by etherification and/or esterification ofthe hydroxy groups in alkylene oxide polymers such as, for example, theacetate of the Z-ethyl exanol-initiated polymer of propylene oxide.Other important classes of synthetic oils include the various esters as,for example, di-(Z-ethylhexyl) sebacate, tricrcsyl phosphate, andsilicate esters such as hexa (2-ethyl butoxy) disiloxane. If desired,the oil can be a mixture of mineral and synthetic oils.

While satisfactory lubricant compositions can be obtained by adding tothe base oil employed only one or more of the polymeric additives of thetype described above, it also falls within the purview of this inventionto provide lubricant compositions which contain not only such polymers,but also other additives such as oiliness and extreme pressure agents,anti-oxidants, corrosion inhibiting agents, blooming agents, thetemperature-viscosity characteristics of the oil. The present inventionalso contemplates the addition to the lubricant composition(particularly when the amount of copolymer employed is relatively small)of detergents and/or anti-wear agents.

Illustrative lubricant compositions of the above type containing thepolymeric additives of the invention in combination with other agentsmay include, for example, from about 0.1 to 10% by weight of alkalineearth metal higher alkylphenate and sulfonate detergents, such ascalcium alkylphenates having an average of approximately 14 carbon atomsin the alkyl group and basic calcium petroleum sulfonate, as well asorganic thiophosphate corrosion and high temperature oxidationinhibitors such as the reaction product of pinene and P and the bivalentmetal dihydrocarbyl dithiophosphates, zinc butyl hexyl dithiophosphateand zinc tetradecylphenyl dithiophosphate in amounts of from about 0.1to by weight of the composition.

The superior properties of these novel lubricant compositions areillustrated by data compiled in the following tables.

In Table I various amounts of polyglutamate are incorporated insolvent-refined 150 neutral mineral lubricating oil in terms of percentby weight, and the improvement in viscosity and the surprisingresistance to shear degradation corresponding to the low percent byweight polyglutamate additive is observed. The V1. is determined by ASTMStandard Method D567-4l. The shear loss is determined by applying shearforces in the form of cavitations induced by ultrasonic waves andmeasuring the change in viscosity at 210 F before and after cavitation.The polyglutamate employed is the trans-esterification reaction productof poly-' -benzyl-L- glutamate and lauryl alcohol, having a compositioncorresponding to approximately 90% polylauryl glutamate and 10%polybenzyl glutamate. Samples Numbers 1 through 5 have 2111 averagemolecular Weight of about 500,000 and sample Number 6 has an averagemolecular weight of about 160,000.

Table I OILPOLYGLUTAMATE SOLUTION PROPERTIES Percent Viscosity Percentby Weight Sayholtlt Shear Loss Sample No. Polygluta- Seconds Viscosity(A Vi cosity mate in Universal Index at 210 F.) 150 N Oil at 210 F.

Table 11 illustrates the superior thickening power of the abovedescribed polyglutamate as compared to commcrically acceptable V.I.improvers. Acryloid 763 is a polymethacrylate V.I. improver having anaverage molecular weight of about 400,000, sold by Rohm & Haas. ParatoneN is a polybutylene VJ. improver having an average molecular weight ofabout 120,000, sold by Enjay Co. The amount of additive that must beincor- O porated in N oil to raise the viscosity of the oil at 210 F. to67.2 SSU is measured and compared.

Table II COMPARATIVE THICKENING rownns Polytzluta Acryloid Paratonc Nmate 763 Weight percent additive required to yield oil otequal viscosity0.5 3.05 3.0

Table III illustrates the superior shear performance of the presentinvention as compared to the above mentioned commercial additives. Theshear loss is determined by the method described above. The oil testedis at an additive concentration that will yield an oil of 67.2viscosity, SSU at 210 F.

From the tests in Table I, it will be seen that each of the illustrativecompositions containing the polyglutamate thickener possess remarkablyimproved viscosity-temperature properties compared to the base oilalone. Further, this improvement in viscosity-temperature behavior isachieved with the incorporation of a surprisingly small percent byweight of the polyglutamate, as is illustrated by Table II above. Bycomparison, commercially acceptable V.I. improvers such as the Acryloidsor Paratones are normally employed in the amount of 1 to 5% by weight ofthe lubricating oil solution, whereas, approximately of a percent byweight of the present invcntion provides sufficient thickening.Specifically, to raise the viscosity of 150 neutral oil to 67.2 SSU at210 F. 6 times more Acryloid 763 or Paratone N is required than isrequired of the polyglutamate thickener, see Table 11.

Similarly, it can be seen from Table III that, for an oil-additivesolution of a viscosity of 67.2 SSU at 210 F. the present inventiondisplays a 2.1 times greater shear strength than Paratone N and a 10.6times greater shear strength than Acryloid 763.

We claim:

1. A lubricant composition comprising a major proportion of an oil oflubricating viscosity and a minor propontion, sufficient to improve theviscosity index of said oil of poly-gamma-esters of optically activeglutamic acid having recurring units of the following formula --NHCH-C0- wherein said gamma ester R radicals are selected from the groupconsisting of 0 to 30 mol. percent benzyl radicals and from 70 to 100mol. percent of alkyl radicals containing from 8 to 18 carbon atoms, themolecular weight of said polyester ranging from 10,000 to 1,000,000 andn being the number of recurring units corresponding to said molecularweight.

2. A lubricant composition comprising a major proportion of an oil oflubricating viscosity and a minor proportion, suflicient to improve theviscosity index of said oil of the poly-gamma-esters of optically activeglutamic acid having recurring units of the following formula --NHCH-O OI: 2): 10 0 R n wherein said gamma ester R radical is selected from thegroup consisting of 0 to 30 mol. percent benzyl radicals and from 70 to100 mol. percent of the lauryl radical, the polyester having a molecularweight of 10,000 to 1,000,- 000 and n being the number of recurringunits corresponding to said molecular weight.

3. A lubricant composition comprising a major proportion of an oil oflubricating viscosity and a minor proportion, sufiicient to improve theviscosity index of said oil of the poly-gamma-esters of optically activeglutamic acid having recurring units of the following formula whereinsaid gamma ester R radical is selected from the group consisting of 0 to30 mol. percent benzyl radicals and from to mol. percent of the tridecylradical, the polyester having a molecular weight of 10,000 to 1,000,000and n being the number of recurring units corresponding to saidmolecular weight.

References Cited in the file of this patent UNITED STATES PATENTS2,368,604 White Jan. 30, 1945 2,752,312 Dixon June 26, 1956

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR PROPORTION OF AN OIL OFLUBRICATING VISCOSITY AND A MINOR PROPORTION, SUFFICIENT TO IMPROVE THEVISCOSITY INDEX OF SAID OIL OF POLY-GAMMA-ESTERS OF OPTICALLY ACTIVEGLUTAMIC ACID HAVING RECURRING UNITS OF THE FOLLOWING FORMULA